Noise suppressor circuit



April I3, E937. J. VAN sLooTEN Y 2,076,803

NOISE SUPPRESSOR CIRCUIT Filed June 23, 1954 2 SheehS-Sheel'l l ./GNL L JAco VAN s ooTEN BY "l x L J Arc APR 13 w37 J. VAN sLooTEN 2,0763

NOISE sUPPRssoR CIRCUIT i Filed June 25, 1934 2 Sheets-Sheet 2 @E ei INVENTOR JACOB `vLOOTEN BY f ATTORNEY 45 5 oscillations. This coupling can be obtained in case the grid of the tube 8 has a constant nega- 55 OFFIQE Noren sUrritEsson omoUrr Jacob van Slooten, Eindhoven, Netherlands, assignor to Radio Corporation of America, a corporation of Delaware Application June Z3, 1934, Serial No. 732,047 In the Netherlands August 30, 1933 3 Claims. (Cl. Z50-20) This invention relates to the noiseless tuning any known manner, for instance, by connecting, of radio receiving sets comprising automatic volas shown in Fig. 1, the anode of the tube I to the urne control of the soundstrength. grid of the tube 2 by means of a condenser 3.

One of the drawbacks inherent to receiving The controlling grid circuit of the tube 2 com- 5 sets having automatic volume control is that upon prises a leakage resistance ll, and in addition a modification of the tuning of the receiver the resistance 5. This resistance is traversed by the sensitivity is altered in such a manner that when anode current of an amplifying tube 6 so that no carrier wave is received the sensitivity, i. e. the grid bias of the demodulator 2 depends on the the amplification factor of the highand/or mesize of the anode current of the tube 6. When 10 dium frequency amplifier forming part of the vthis current is large the controlling grid of the l0 receiver attains its maximum value. Owing to tube 2 attains such a large negative voltage with this noises caused by atmospheric discharges or respect to the cathode that this tube can no longer other noises, for instance, due to electron emisact as a demodulator. If, on the contrary, the' sion in amplifying tubes (Schrott-effect), are'amanode current of the tube 6 is small then the plied to ahigh extent and consequently manifest negative voltage of said controlling grid is small l5 themselves in an annoying manner during the relatively `to the cathode so that the received time in which no carrier wave is received. Such oscillations can be rectified in a normal manner noises manifest themselves not only in the abby the tube 2. This rectification can be ensured sence of a carrier wave, but also during the adboth by anode and by grid rectification.

justment of the receiving set when it is tuned to As has already been stated the anode of the 20 a frequency lying between two carrier waves. high or medium frequency amplifying tube I is The present invention has for its purpose to coupled with the grid of the tube 2, and in addiprovide means for suppressing noises in the retion to the grid 'I' of a rectifying tube 8 by ceiver in the absence of a carrier wave, and for meansof a condenser 1. Due to this, a high, or

ensuring at the same time noiseless tuning of medium, frequency voltage drop occurs through 25 the receiver. a resistance 9 lying between the grid and the According to the invention this is ensured in cathode of the tube 8, this drop causing a rectified a radio receiving set with automatic volume concurrent through the resistance III inserted in the trol during the time in which no carrier wave, or anode circuit of the tube 8. This resistance is only a carrier wave having an amplitude below shunted by a condenser II having such a capacity 30 a definite value', is received by varying the pothat no, or substantially no, high or low fretential of one of the electrodes of a thermionic quency voltage drop can occur through the retube for demodulating, or for converting the fresistance. The direct voltage drop through the quency of the received oscillations in such a' resistance II), whose value depends on the ammanner that this tube is entirely or substanplitude of the high or medium frequency oscilla- 35 tially rendered inoperative. tions set up at the grid of the` tube 8 and conse- The novel features which I believe to be charquently also depend on the amplitude of the reatelisi 0f my IlVeIltOIl are Set fOrth n parceived carrier wave, determines the voltage of i ticularity in the appended claims. The inventhe grid of the tube ii relatively to the cathode,

40 tion itself, however, both as to its organization and thus regulates the anode current traversing 40 and method of operation, will best be understood the resistance 5. The end of the resistance I0 by reference to the following description taken in connected to the anode of the tube 8 is at the connection with the drawings, in which I have same time connected to the controlling grid cirindicated dagrammatically several circuit orcuit of the amplifying tube I as indicated by the ganizations whereby my invention may be cartrunk line I2. Also the grid circuits of further 45 ried into effect. high and/or medium frequency amplifying tubes The invention will be more clearly understood preceding the tube IA may be connected to the by reference to the accompanying drawings, Figs. line I2.

1, 2 and 3 thereof representing, by way of ex- The working of the arrangement set out is as 5o ample, different embdmentsfollows: In the absence of a carrier wave no high 50 In Fig. l of the drawings l denotes a high, or medium frequency oscillations occur in the or medium, frequency amplifying tube of a reanode circuit of the tube I, so that the grids of ceiving set; the tube is coupled with a succeeding the tubes 2 and 8 have no alternating tension tube 2 serving for demodulation of the received relatively to the corresponding cathodes. In this Cil tive bias which is determined by the source of grid bias voltage, and has such a value that no anode current flows in the tube 8 due to which no voltage is present between the grid and the cathode of the tube 6. Consequently anode current flows in this tube 6 which current causes a voltage drop through the resistance 5 due to which the tube 2 is rendered inoperative.

In this manner it is impossible that, although the amplification factor of the high and/cr medium frequency amplifying tubes (due to the absence of a voltage drop through the resistance I0 which drop regulates the amplification factor as has been set out above) has its maximum Value, disturbances caused by atmospheric or other phenomena reach the low frequency amplifier and be successively reproduced, for instance, by a loudspeaker.

When receiving a carrier wave alternating tensions are set up through the resistance 9 which tensions are rectified by the tube 8, which acts as an anode rectifier, and cause a direct voltage drop through the resistance Ii! in the anode circuit of said tube. This voltage drop first regulates the amplication factor of the amplifying tube I, and of the preceding amplifying tubes, in such a manner that the amplitude of the alternating tensions set up in the anode circuit of the amplifying tube I always remains substantially constant independently of the amplitude of the received oscillations. Secondly, the grid of the tube 6 becomes highly negative due to the voltage drop through the resistance Ill so that the anode current in this tube is entirely, or almost entirely, suppressed due to which no voltage drop occurs through the resistance 5. In this manner the demodulator 2 can act in a normal manner, and rectifies the amplified received oscillations.

Another form of construction of the circuit arrangement according to the invention is represented in Fig. 2 in which, just as in the arrangement shown in Fig. 1, the noiseless tuning is ensured by rendering the controlling grid inoperative by a suitable negative voltage set up at the controlling grid during the time in which no carrier wave is received. The difference from the arrangement shown in Fig. 1 is that in the arrangement represented in Fig. 2 a binode, or multi-section tube, 6' is used for achieving noiseless tuning. Furthermore both arrangements differ from each other in that in the arrangement shown in Fig. 2 the working of the device for obtaining noiseless tuning is more independent of the working of the device serving for the automatic volume control.

The binode tube 6' comprises an amplifying system, or section, consisting of an indirectly heated cathode I3, a grid III and an anode I5, and, in addition, a rectifying system, or section, having an anode I6 which system and the amplifying System have a common cathode. Between the anode I6 and the cathode I3 is connected a resistance 9' which is coupled With the anode circuit of a high, or medium, frequency amplifying tube I through a condenser 'I". In the presence of high, or medium, frequency oscillations in the anode circuit of the tube I an alternating tension is set up in the anode circuit of the tube I through the resistance, which tension is rectified by the diode section of tube 6 and causes a direct voltage drop through the resistance 9. This voltage drop controls through a resistance I0 the controlling grid I4 of the amplifying system of tube 6', and consequently also the anode current thereof traversing the resistances 5' and Il. The voltage drop through the first mentioned resistance determines the grid bias of the demodulating tube 2 in such a manner that when the anode current flows in the tube 6' the demodulator 2 is inoperative. The voltage drop through the resistance II regulates the grid voltage of a tube 8 in whose anode circuit a resistance I9 is inserted. The voltage drop across this resistance regulates in a known manner the amplification factor of the amplifying tube I, and, if desired, the amplification factor of the preceding amplifying tubes.

The arrangement shown in Fig. 2 may furthermore be completed by providing a condenser I'I through which high or medium frequency oscillations are supplied to the controlling grid of the tube 8', and by connecting a resistance I'I in the line I 8. In this case the tube 8 acts at the same time as an anode-detector for the high or medium frequency oscillations due to which the regulating working of the automatic volume control is still increased.

In this case it is possible by short-circuiting the resistance II to render the Working of the tube serving for the automatic volume control entirely independent of the working of the tube serving for noiseless tuning.

Fig. 3 of the drawings represents an arrangement in which the device for the automatic volume control, and the device for the noiseless tuning are entirely independent of each other. In this arrangement, just as in that shown in Fig. 2, a binode 23 is used which acts as a diode-rectifier and as an anode rectifier. For this purpose the output circuit of a high, or medium frequency, amplifier is coupled through condensers 21 and 29 with the anode of the diode, and with the controlling grid of the triode section of the binode 28. The controlling grid circuit comprises a resistance 20 which is connected through a source of Voltage 2| to the cathode of the binode 28. This voltage source 2| impresses such a negative bias on the controlling grid that anode rectification occurs in the anode circuit of the tube 28. The direct voltage drop thus occurring through the resistance I2 in the anode circuit of the binode 28 regulates the amplification factor of the amplifying tube I.

The direct voltage drop occurring through a resistance 23, due to the rectification in the diode system, controls the grid of a tube 26 in the anode circuit of which a resistance 25 is inserted which, just as in the arrangements shown in Figs. 1 and 2, regulates the grid voltage of the demodulator tube 2.

The Working of the arrangement shown in Figs. 2 and 3 entirely corresponds to that of the arrangement represented in Fig. 1, so that it need not be described here in detail. It will be readily appreciated that, although in the arrangements shown in Figs. 1, 2 and 3, the noiseless tuning and the suppression of noises during the time in Which no carrier wave is received is ensured by adding a negative bias to the controlling grid of the thermionic tube serving for demodulation, it is also possible to render the demodulator inoperative by applying a bias to one of the other tube electrodes.

Furthermore, with superheterodyne receiving sets the thermionic tube serving for frequency conversion can be rendered inoperative by applying a suitable bias to one of the electrodes which measure may, if desired, be applied simultaneously with the rst mentioned measure. Furthermore, it is possible Without any further means by using suitable biases for the tubes in the arrangements, according to the invention, to ensure a retarded Working of the demodulator and of the automatic volume control. Y

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made Without departing from the scope of my invention, as set forth in the appended claims.

What is claimed iszl. In combination with a signal amplier and a demodulator of the plate rectication type, a plate rectication detector including a resistor in its space current path, an amplier gain control connection from the plate side or" the resistor to a gain control electrode of the amplifier, means for impressing signal energy upon said detector, a diode rectication circuit including an im pedance, means for impressing signal energi7 upon the diode electrodes, an electron discharge device circuit having its input electrodes connected to points on said impedance such that space current now of the device is prevented when signals are impressed on the diode circuit, a second resistor in the space current path of the said device, and the input electrodes of the demodulator being connected to points on the last resistor such that demodulation is prevented when the space current of said device flows and means responsive to plate current variation of said discharge device for regulating the space current flow of saiddetector.

2. In combination with a signal amplifier and a demodulator of the platerectication type, a plate rectification detector including a resistor in its space current path, an amplifier gain control connection from the plate side of the resistor to a gain control electrode of the amplifier, means for impressing signal energy upon said detector, a diode rectication circuit including an impedance, means for impressing signal energy upon the diode electrodes, an electron discharge device circuit having its input electrodes connected to points on said impedance such that space current flow of the device is prevented when signals are impressed on the diode circuit, a second resistor in the space current path of the said device, and the input electrodes of the demodulator being connected to points on the last resistor such that the demodulation of signals received from the amplier is prevented when the space current of said device flows, a third resistor disposed in the space'current path of said device, the input electrodes of said detector being connected to points of said third resistor whereby variations in amplitude of signals impressed upon the diode circuit causes control oi the detection action of 'said detector.

3. In combination with a signal amplier and a demodulator of the plate rectication type, a plate rectication detector including a resistor in its space current path, an ampliiier gain control connection from the plate side of the resistor to a gain control electrode of the amplifier, means for impressing signal energy upon said detector, a diode rectication circuit including an impedance, means for impressing signal energy upon the diode electrodes, an electron discharge device circuit having its input electrodes connected to points on said impedance such that space current flow of the device is prevented when signals are impressed on the diode circuit, a second resistor in the space current path of the said device, and the input electrodes of the demodulator being connected to points on the last resistor such that the demodulation of signals received from the amplifier is prevented when the space current of said device iloWs and means responsive to plate current variation of said discharge device for regulating the space current flow of said detector, the electrodes of said device being included in a common tube envelope housing the diode electrodes, and the cathode of thediode and device being a common one.

JACOB VAN SLOOTEN. 

